Variety, Constraint, and the Law of Requisite Variety

A subject in which the concept of a set plays an essential part is that of “communication”, especially in the theory developed by Shannon and Wiener. At first, when one thinks of, say, a telegram arriving, one notices only the singleness of one telegram. Nevertheless, the act of “communication” necessarily implies the existence of a set of possibilities, i.e. more than one, as the following example will show.